微量稀土元素对奥氏体不锈钢21-4N显微组织及碳化物的影响

通过对21-4N钢添加微量稀土Ce元素,分析不同Ce含量对21-4N钢铸态、锻态下的显微组织的影响。结果表明:适量稀土Ce元素的加入,可以显著细化铸态树枝晶间距、"类珠光体"团及一次碳化物M_7C_3,改善铸态"类珠光体"形貌,减少一次碳化物数量;显著细化锻态奥氏体晶粒尺寸。当Ce含量过高,铸态"类珠光体"团粗化、一次碳化物数量增加;锻态奥氏体粗化。Ce元素含量0.011%≤w(Ce)≤0.015%时,21-4N钢的铸态"类珠光体"团尺寸小、形状球化,一次碳化物细小且数量增加;锻态奥氏体晶粒细小。     

2%铝质量分数超高碳钢的球化退火工艺

 为获得完全球化的超高碳钢组织,基于离异共析转变机制对2%铝质量分数超高碳钢进行球化退火工艺研究。研究发现,由于成分的不均匀性,超高碳钢锻态组织由片层间距不一致的珠光体和网状碳化物组成,单纯使用离异共析工艺无法使其完全球化;2%铝质量分数超高碳钢锻态组织网状碳化物厚度在1 μm以下,[Acm]温度以下正火即可获得片层均匀细小的珠光体并消除网状碳化物;提高正火温度能显著减少正火组织中长条和短棒状碳化物的数量,利于获得较好的球化组织。2%铝质量分数超高碳钢经900～925 ℃正火后在830 ℃奥氏体化并在760 ℃等温4 h后获得了由超细铁素体＋细小球状渗碳体组成的完全球化组织。     

V和Ti在高碳钢中的应用

研究了V、Ti在预应力钢绞线及钢丝用高碳钢线材中的应用。高碳钢盘条中加入微量的V、Ti,在降低了珠光体相变温度的同时使珠光体相变与贝氏体相变温度区间发生分离;V的加入可以在细化珠光体片层间距的同时,抑制晶界连续渗碳体的形成。V、Ti在高碳钢中主要以复合碳氮化物的形式在晶界铁素体及珠光体片层间弥散析出,同时有部分V以合金碳化物的形式存在于渗碳体片层中。高温区析出的Ti(C,N)对奥氏体晶粒的长大具有显著的抑制作用,V主要在低温区以碳氮化物的形式起到析出强化的作用,另有部分V原子与Cr类似,与渗碳体结合形成合金碳化物,起到了强化渗碳体的作用。     

RE复合变质处理对高铬合金铸铁组织及性能的影响

采用光学显微镜、扫描电镜和力学性能检测设备等研究了RE复合变质处理对高铬合金铸铁显微组织和力学性能的影响。试验结果表明,变质处理可以细化基体组织,消除柱状树枝晶,改善碳化物形态和分布,使碳化物棱角得到钝化,碳化物更加细小,从而使高铬合金铸铁力学性能得到提高,与未变质高铬合金铸铁相比,变质高铬合金铸铁的硬度和冲击韧度分别提高了1.74%和27.27%,达到了HRC64.0和4.2 J/cm2。     

提高钨合金铸铁磨球使用性能的研究

以我们近年开发的钨合金铸铁磨球为基础,探讨了采用稀土变质处理以提高其使用寿命的可能性。研究结果表明:钨合金铸铁磨球经适量稀土变质处理后。共晶碳化物由网状分布变成断网状分布,磨球冲击韧性显著提高,硬度略有上升,耐磨性明显改善,冲击疲劳寿命显著提高,磨球各项指标,达到甚至超过了高铬铸铁球的水平。可见用稀土处理提高钨合金铸铁磨球使用性能将是可行的。     

白口铁的稀土变质处理对热处理时碳化物团聚化的影响

从改变共晶碳化物形貌的角度研究了稀土变质处理与热处理两者之间的内在联系及相互作用。结果表明,变质后再进行热处理可以显著地加速白口铁共晶碳化物的溶解,断网与团聚化,并明显地提高韧性,综合运用变质处理和热处理是改变白口铁共晶碳化物网状分布,提高韧性的有效途径。     

合金化和球化工艺对超高碳钢组织和性能的影响

 研究了合金化和球化工艺对超高碳钢组织和性能的影响。用扫描电子显微镜、透射电子显微镜和能谱仪观察了钢的组织形貌和元素分布。结果表明：在碳和铬含量相同的超高碳钢中加入同量的合金元素铝和硅时,铝可明显抑制锻造组织中网状或粗大的颗粒状碳化物的析出、细化珠光体组织和控制石墨形成。UHCS 213Si和UHCS 261Al钢经850 ℃×3 h球化退火处理后,都能得到较好的球化组织,其力学性能分别为：UHCS 213Si钢,Rm=1 033 MPa,Re=734 MPa,A=149%;UHCS 261Al钢,Rm=973 MPa,Re=677 MPa,A=182%。     

稀土处理钢中晶内铁素体的形成及其对性能的影响

测定了稀土脱氧和铝稀土复合脱氧钢焊接热影响区(HAZ)的连续冷却转变曲线,分析了2种钢中的夹杂物种类及其HAZ的显微组织和常温冲击韧性。得到如下结论:稀土脱氧使钢中主要夹杂物从Mn S转变为RE2O2S+Mn S,而铝稀土复合脱氧钢中夹杂物主要是Ce Al O3+Ce2S3+Mn S。稀土脱氧钢HAZ中能获得晶内铁素体的冷速较宽,约为0.5~7.5℃/s。铝稀土复合脱氧钢HAZ获得晶内铁素体组织较稀土脱氧钢要困难一些,适合晶内铁素体形成的冷速变窄为1~3℃/s,HAZ中晶内铁素体的含量明显低于稀土处理钢,Al脱氧弱化了稀土处理对钢HAZ组织的改善作用。焊接热输入线能量为100 k J/cm时,稀土脱氧能够明显改善钢HAZ的室温冲击韧性。     

原位观察铌对高碳钢珠光体相变的影响

 为了研究微合金元素铌(Nb)对高碳钢中珠光体相变的影响,在高温激光共聚焦显微镜下原位观察了不含铌和含铌高碳钢连续冷却过程中珠光体动态形核和长大行为。结果表明,在高碳钢中添加铌增加了珠光体形核点的数量,这是因为铌提高珠光体单位面积形核数量。同时,铌元素减慢珠光体长大速率是由于铌显著阻碍珠光体长大,但当铌质量分数超过0.014%后,阻碍珠光体长大速率的效果不再进一步增加。从以上结果可知,在高碳钢中添加铌促进珠光体形核,但是减慢珠光体长大速率。所以,为了更加准确地研究铌元素对珠光体相变的影响,选用不含铌及铌质量分数为0.027%的两种高碳钢,在Gleeble-3500热模拟试验机上进行与高温原位观察试验相同试验工艺的热膨胀试验。通过热膨胀试验发现,铌的添加增大过冷度,导致降低了珠光体相变温度区间,但是铌显著阻碍碳在奥氏体中的扩散系数,所以铌减慢珠光体长大速率。另外,铌减慢连续冷却条件下的珠光体相变动力学,推迟珠光体相变,从而降低珠光体相变速率,表明铌对珠光体长大的阻碍作用强于其对珠光体形核的促进作用。因此,在高碳钢中,铌元素的添加推迟珠光体相变。此外,铌的添加增大过冷度,使含铌高碳钢的珠光体片层细化,提高了含铌高碳钢的硬度,但在铌质量分数超过0.014%后,细化效果不再进一步增强。     

稀土Y、Ce对钼合金力学性能的影响

实验以MoO2和Ce(NO3)3.6H2O、Y(NO3)3.6H2O为原料,通过固-液掺杂、还原、烧结、拉伸制备钼合金丝。通过XRD、扫描电镜以及力学性能试验,研究了稀土元素Y、Ce在粉末及钼合金中的存在形式以及对钼合金力学性能的影响。结果表明:Y、Ce元素分别以CeO2和Y2O3形式存在于钼粉中,Y对钼粉颗粒长大的抑制效果高于Ce;钼合金中,稀土Y和Ce作用不同,Y抑制晶粒的长大,延迟烧结;而Ce促进烧结,使烧结完全致密化;钼合金丝中,CeO2质点以纤维状存在,有利于提高钼丝的塑性,而Y2O3质点以球状颗粒存在,钼合金丝的室温和高温抗拉强度较高。Y、Ce的共同作用,MYCe合金丝综合力学性能好。     

A Coupled Thermodynamic Model for Prediction of Inclusions Precipitation during Solidification of Heat-resistant Steel Containing Cerium

A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microsegregation of solute elements during solidification of heat-resistant steel containing cerium was established.Then the model was validated by the SEM analysis of the industrial products.The type and amount of inclusions in solidification structure of 253 MA heat-resistant steel were predicted by the model,and the valuable results for the inclusions controlling in 253 MA steel were obtained.When the cerium addition increases,the types of inclusions transform from SiO2 and MnS to Ce2O3 and Ce2O2S in 253 MA steel and the precipitation temperature of SiO2 and MnS decreases.The inclusions CeS and CeN convert to Ce2O3 and Ce2O2S as the oxygen content increases and Ce2O3 and CeN convert to Ce2O2 S,Ce3S4,and MnS as the sulfur content increases.The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increases.There is only a small quantity of inclusions containing cerium in 253 MA steel with high cleanliness,i.e.,low oxygen and sulfur contents.By contrast,a mass of SiO2,MnS and Ce2O2 S are formed in steel when the oxygen and sulfur contents are high enough.The condition that MnS precipitates in 253 MA steel is 1.2 w[O]+w[S]0.01%and SiO2 precipitates when 2 w[O]+w[S]0.017%(w[S]0.005%)and w[O]0.006%(w[S]0.005%).     

Effect of Ce on Inclusions and Impact Property of 2Cr13 Stainless Steel

 The effect of Ce on inclusions and impact toughness of 2Cr13 stainless steel were studied by SEM and electron spectroscopy. Thermodynamic calculation was used to analyze the formation of RE inclusions in 2Cr13 stainless steel. The result shows that Al2O3 and MnS can be entirely replaced by Ce2O2S and CeS. Fracture is changed from cleavage to ductile fracture by adding Ce to the 2Cr13 stainless steel, and the spherical rare earth oxysulfide inclusions-Ce2O2S in the dimple are the main factors. The transverse impact value of 2Cr13 stainless steel has been improved obviously by rare earth. The transverse impact value of RE-2Cr13 is increased 55.46% at the temperature of -40℃, comparing with 0RE-2Cr13.     

Behaviors of Lanthanum and Cerium on Grain Boundaries in Carbon Manganese Clean Steel

The behaviors of La and Ce on gram boundaries in carbon manganese clean steel were investigated by high-reso- lution transmission elecetron microscope （HRTEM）, scanning elecetron microscopy（SEM ）, energy dispersive spectrometer （EDS） and X-ray diffraction（XRD） analysis. The existing forms of rare earths （RE） in clean steel were as follows： dissolved in sohd solution, forming inclusion or second phase containing RE （RE-Fe-P, La-P, Fe-La eutectic and Fe-Ce phase）. The dissolved La or Ce segregated at grain boundaries. The segregation of both S and P at gram boundaries was reduced with suitable RE content. The impact toughness of the steel was improved obviously. La and Ce had effecets on purifying molten steel and modifying inclusions in clean steel, whereas with excessive La or Ce, La-Fe-P, La-P and Fe-La eutecetic phase or Ce-Fe-P and Fe-Ce intermetallic compound would form along grain boundaries, causing the impact energy to decrease significantly.     

含钛中碳钢中钛氧化物析出热力学分析

摘要：以含钛中碳钢为研究对象,从热力学的角度分析了含钛中碳钢中钛氧化物析出行为,结果表明：浇注温度为（1535±10）℃且钢中溶解氧含量大于0.003%（质量分数,余同）时,低钛中碳钢中的溶解Ti可与钢中的溶解氧反应生成Ti3O5、Ti2O3,生成TiO2、TiO夹杂的可能性较小;高钛中碳钢中的溶解Ti可与钢中的溶解氧反应生成Ti3O5、Ti2O3、TiO2和TiO夹杂;同时钢中的溶解Ti能够还原钢中的SiO2、MnO、Cr2O3夹杂物并生成TiO2夹杂;低钛中碳钢中不会生成TiC、TiN、TiS和Ti4C2S2夹杂;高钛中碳钢中可能会生成TiN和Ti4C2S2夹杂。对于低钛中碳钢,控制钢中较低的溶解氧含量（<0.002%）,对于高钛中碳钢,控制钢中较低的溶解氧含量（<0.0007%）及较少的Cr2O3、MnO、SiO2夹杂数量,可有效抑制含钛中碳钢中高熔点含钛夹杂物的生成,实现中碳钢低成本钛合金化及相关连铸工艺开发。     

Ce对2.9%Si-0.8%Al无取向硅钢夹杂物变质的影响

研究了添加单一稀土元素Ce后2.9%Si-0.8%Al无取向硅钢中夹杂物的变质机理。依据冶金热力学理论计算了Ce添加后,钢液中可能生成的夹杂物种类,分析了各种夹杂物存在的稳定性和相互转化的条件。在此基础上,利用SEM、EDS研究了Ce对无取向硅钢中夹杂物数量、尺寸、形貌及类型的影响。结果表明:适量的Ce显著降低了无取向硅钢中微细夹夹杂物(小于1μm)的数量,增加了粗大夹杂物(2~5μm)数量;Ce使AlN、Al_2O_3等夹杂物变性为球状的CeO_2S_2+AlN、CeS+CeAlO_3和CeS+Al_2O_3等复合夹杂物,有效抑制了钢中MnS的析出。     

Effect of refining slag containing Ce_2O_3 on steel cleanliness

The effect of pre-melting refining slag containing different contents of Ce2O3 on the absorption and modification of Al2O3 inclusion in an Al-killed steel was investigated through the slag/steel reaction experiment at 1600 oC.It was found that the replacement of 10 wt.% Al2O3 with Ce2O3 for 50 wt.%CaO-33 wt.%Al2O3-7 wt.%MgO-10 wt.%SiO2 refining slag promoted the slag absorption ability of alumina inclusion,which made the total oxygen content determined by infrared absorption method decrease from 100 to 25 ppm in 15 min.The Mg-Al-Ce-O type inclusion was also detected in the as-solidified samples by scanning electron microscopy(SEM).Thermodynamic analysis indicated that the Ce2O3.Al2O3 type inclusions would be formed with the cerium content in the range of 6.9 ppb to 3.6 ppm when the content of aluminum was 0.01 wt.%.     

Si-Mn系超高强度热成形淬火钢板的点焊性能

 采用不同的点焊工艺参数对研发的1700MPa级Si-Mn系热成形淬火钢板与低碳钢板DC04进行异种材料之间点焊,并对焊接接头的拉伸性能、显微硬度分布及微观组织特征等进行了分析。结果表明,焊接电流对点焊接头熔核直径和抗剪强度具有显著的影响,而焊接时间的影响相对较小。超高强度钢板侧的热影响区存在两个明显的软化区和硬化区,即在靠近母材处存在一个硬度明显低于母材的软化区,其组织为回火马氏体;在靠近熔核处存在一个硬度明显高于母材的硬化区,其组织为细小的马氏体。点焊接头熔核部位为柱状粗大马氏体组织,其硬度明显低于超高强度钢板母材且远高于低碳钢板母材。低碳钢板热影响区低的硬度和明显粗化的铁素体组织,使得点焊接头单向拉伸时均从低碳钢板的热影响区一侧破断。     

Coarsening of Inter- and Intra-granular Proeutectoid Cementite in an Initially Pearlitic 2C-4Cr Ultrahigh Carbon Steel

Metallurgical and Materials Transactions A - We have examined spheroidization and coarsening of cementite in an initially pearlitic 2C-4Cr ultrahigh carbon steel containing a cementite network....     

Evolution of Al2O3 inclusions by cerium treatment in low carbon high manganese steel

The influence of cerium (Ce) treatment on the morphologies, size and distributions of Al2O3 inclu-sions in low carbon high manganese steel was investigated by OM, SEM-EDS and theoretical calcula-tion.The results showed that Ce can modify the morphologies and types of Al2O3 inclusions.After Ce treatment, the irregular Al2O3 inclusions were replaced by smaller and dispersive spherical cerium oxysulfides.The effects of treatment time and Ce content on the evolution of Al2O3 inclusions were examined.It indicated that Al2O3 inclusions were wrapped by rare earth inclusions to form a ring like shape Ce-enriched band around the inclusions.Model was established to elucidate the evolution mech-anism of Al2O3 inclusions.Evolution kinetics of inclusions was discussed qualitatively to analyze the velocity controlled step.It was found that diffusion of Ce3 + and Al3 + in solid inclusion core and the formed intermediate layer would be the limited step during the evolution process.     

Effect of Ultrasonic Treatment on the Solidification Structure of High Carbon Steel Containing Rare Earth Elements

The influence of ultrasonic treatment on solidification structure of high carbon steel with the addition of rare earth Ce was investigated. Effects of various ultrasonic power and treatment time on the solidification structure were studied. The results showed that ultrasonic treatment could obviously refine the solidification structure of high carbon steel containing rare earth Ce. With increasing ultrasonic power, a more refined structure could be obtained. When the ultrasonic power exceeded a certain degree, the effects of ultrasound on structure refinement were not increased significantly. Dendrites developed in the solidifying structure when the ultrasonic treatment times were 0 s and 20 s. However, a uniform and refined dendrite structure was obtained after ultrasonic treatment for 40 s. The solidification structure refinement of high carbon steel containing Ce was ascribed to the increased amount and decreased size of rare earth oxides and oxysulfides by ultrasonic cavitation, which could serve as heterogeneous nuclei of a new crystal phase.